Washington (CNN) - The top Democrat on the House Oversight and Government Reform Committee accused the panel's chairman, Representative Darrell Issas R-California, of selectively leaking documents related to testing done on HealthCare.gov, the troubled Obamacare website.

Rep. Elijah Cummings D-Maryland, made the allegation Friday amid a battle over Issa's request for testimony from the Obama administration's top technology officer, Todd Park, at a hearing scheduled for next week. Issa has hinted he may subpoena Park to compel his testimony.Follow @politicalticker

Issa said that performance stands in contrast with previous statements made to the committee by Park who insisted the site could handle a much larger workload, close to 60,000.

But Cummings said Issa failed to disclose that another top administration technology official, Henry Chao, the deputy chief information officer at the Centers for Medicare and Medicaid Services, backed up Park's testimony in a briefing with the committee's staff on November 1.

"You appear to be conflating the results of a much smaller testing environment with final production testing of the system at full capacity," Cummings said in a letter to Issa.

"Based on information obtained by the Committee, it appears that you fundamentally misunderstood or mischaracterized the document you released to the press," Cummings also wrote. "It is unclear why you did not disclose the information Mr. Chao provided."

According to portions of a transcript with Chao that Cummings' office released, the 1,100 projection was only a sample size, not the projection for the full production environment.

Chao further explained the process in the transcript, saying in "performance testing, you introduce (a) number of virtual users."

"Two hundred, 500, 1,000. You know, you're trying to introduce as many as you can handle in the performance testing environment to see where the breakpoint is," he continued. "And then, once you achieve that breakpoint, then you extrapolate, you know, from that how many concurrent users, how many concurrent sessions. Because you don't have a performance testing environment that equals 100 percent the production environment."

Hitting back, Issa's committee said Cummings, himself, left out a key portion of the testimony: Chao's response when he was asked “How many [registrations per hour] could it handle on October 1st?”.

"Maybe 8,000? Somewhere under 10,000," he said, according to Issa's office. "I don't have the exact metrics, but I know that it wasn't 30,000 registrations per hour."

A spokesperson for the committee, Caitlin Carroll, said in a statement that "if Ranking Member Cummings genuinely wants to be seen as a partner in oversight, he should start acting like it instead of using his position to twist facts and create false distractions on behalf of the Administration."

In a letter to Issa on Wednesday, White House officials said Park was too busy to testify at next week's hearing.

Park is "currently occupied full time on the critically important work of improving the website for the millions of Americans seeking affordable health insurance options," the White House wrote in a letter to Issa dated November 6, suggesting instead a date next month.

Issa's panel was set to hear from Park next Wednesday, along with other technology experts from the Department of Health and Human Services, the Centers for Medicare and Medicaid Services, and the Office of Management and Budget, who are working to repair HealthCare.gov.

"His testimony needs to be scheduled at a time that is less disruptive to that work," wrote Donna Pignatelli, the White House's assistant director for legislative affairs, who added later that "pulling him away…even for a short time at this stage would be highly disruptive and would risk slowing the progress that has been made thus far to fix identified issues with the website."

Issa responded with a letter urging Park to reconsider his decision, saying the committee may use its power to compel him testify he refuses to attend.

"Your role in the development and rollout of HealthCare.gov...uniquely positions you to provide testimony that will be valuable for both Congress and the public," Issa said in the letter. "Thus, your participation at the hearing is imperative."